Canonical functions for dispersal-induced synchrony

Two processes are universally recognized for inducing spatial synchrony in abundance: dispersal and correlated environmental stochasticity. In the present study we seek the expected relationship between synchrony and distance in populations that are synchronized by density-independent dispersal. In the absence of dispersal, synchrony among populations with simple dynamics has been shown to echo the correlation in the environment. We ask what functional form we may expect between synchrony and distance when dispersal is the synchronizing agent. We formulate a continuous-space, continuous-time model that explicitly represents the time evolution of the spatial covariance as a function of spatial distance. Solving this model gives us two simple canonical functions for dispersal-induced covariance in spatially extended populations. If dispersal is rare relative to birth and death, then covariances between nearby points will follow the dispersal distance distribution. At long distances, however, the covariance tails off according to exponential or Bessel functions (depending on whether the population moves in one or two dimensions). If dispersal is common, then the covariances will follow the mixture distribution that is approximately Gaussian around the origin and with an exponential or Bessel tail. The latter mixture results regardless of the original dispersal distance distribution. There are hence two canonical functions for dispersal-induced synchrony     

Bayesian nonparametric quantile process regression and estimation of marginal quantile effects

Flexible estimation of multiple conditional quantiles is of interest in numerous applications, such as studying the effect of pregnancy-related factors on low and high birth weight. We propose a Bayesian nonparametric method to simultaneously estimate noncrossing, nonlinear quantile curves. We expand the conditional distribution function of the response in I-spline basis functions where the covariate-dependent coefficients are modeled using neural networks. By leveraging the approximation power of splines and neural networks, our model can approximate any continuous quantile function. Compared to existing models, our model estimates all rather than a finite subset of quantiles, scales well to high dimensions, and accounts for estimation uncertainty. While the model is arbitrarily flexible, interpretable marginal quantile effects are estimated using accumulative local effect plots and variable importance measures. A simulation study shows that our model can better recover quantiles of the response distribution when the data are sparse, and an analysis of birth weight data is presented.     

Two Methods for reconstructing the empirical mortality profile

This paper goes one step beyond the age determination of the individual skeleton. It presents two methods for the reconstruction of the distribution of the age at death in a sample of skeletons. It is shown that the maximum likelihood method, in spite of certain weaknesses, is superior to the traditionally used proportional method, especially in situations when the analyzed sample consists of skeletons with very different conditions of preservation and thus age intervals of differing lengths. The maximum likelihood method eliminates a bias towards increased average age at death which is introduced by the proportional method. An analysis of an empirical example indicates that the difference between results obtained using the two methods increases with increasing age.     

Evolution of senescence: Natural increase of populations displaying gompertz- or power-law death rates and constant or age-dependent maternity rates

Several hypothetical populations which differ in degrees of senescence are compared with respect to their rates of natural increase. The rate of natural increase is employed as a measure of selective advantage. The populations are characterized by their maternity and death rates, expressed as functions of age. Maternity rates are described by constant or quasi-human, age-dependent functions. Death rates are described by constant, Gompertzian (exponential) or power functions. Longevity functions, representing the probability of survival to a specific age, are obtained by integrating the death rate functions. The degree of senescence of a population is measured by the rapidity of ascent of its death-rate function or by the rectangularity of its longevity function. The increase in death rate late in life which constitutes senescence is compensated by a decrease in death rate early in life. The balance between the two changes in rate is, by assumption, such that the mean value of the longevity function is independent of the degree of senescence. This assumption makes it possible to separate the effects produced by the evolution of senescence from those caused by changes in longevity.The rate of natural increase is obtained by numerical solution of an integral characteristic equation. The results show that senescence is advantageous in all populations except those in which the maternity function is constant and the size is declining at a rapid rate. When the parameters entering into the longevity functions have values such that the functions approximate human longevity data, the improvement in the rate of natural increase resulting from senescence closely approaches limiting values obtained with the use of a precisely rectangular longevity function. Other results support the observation that reproduction at an early age confers greater selective advantage than equivalent reproduction later in life.     

Demography in stochastic environments. I. Exact distributions of age structure

The steady state distribution of age structure is studied for populations with two age classes and stochastic vital rates. For a serially uncorrelated dichotomic vital rate the distribution of age structure is found analytically to be a singular steplike function; outside a specific region of vital rate values the singular function crosses a threshold to a smooth function. For a vital rate following a correlated two state Markov process the joint distributions of age structure and environment are found analytically to be singular steplike functions; again a threshold marks a transition to a smooth function. For fecundities which are serially uncorrelated but continuously distributed the age structure distribution is obtained as a smooth analytic function for all parameter values. These explicit results have applications to studies of age structure and average growth rate.     

Distribution-free Estimation of a Monotonic pth Quantile Function

When analyzing biological data sets, a frequent problem is to estimate the pth quantile of a distribution, when that quantile is assumed to depend on a covariate; in the present paper the dependence of the quantile on the covariate is assumed to be monotonic. Some properties of an isotonic pth quantile regression, considered as an estimator of an increasing pth quantile function, are presented.     

Survival and aging in the wild via residual demography

Information about the age distribution and survival of wild populations is of much interest in ecology and biodemography, but is hard to obtain. Established schemes such as capture-recapture often are not feasible. In the proposed residual demography paradigm, individuals are randomly sampled from the wild population at unknown ages and the resulting captive cohort is reared out in the laboratory until death. Under some basic assumptions one obtains a demographic convolution equation that involves the unknown age distribution of the wild population, the observed survival function of the captive cohort, and the observed survival function of a reference cohort that is independently raised in the laboratory from birth. We adopt a statistical penalized least squares method for the deconvolution of this equation, aiming at extracting the age distribution of the wild population under suitable constraints. Under stationarity of the population, the age density is proportional to the survival function of the wild population and can thus be inferred. Several extensions are discussed. Residual demography is demonstrated for data on fruit flies Bactrocera oleae.     

Solvent effects on the secondary structure of the membrane-active zervamicin determined by PELDOR spectroscopy

Zervamicin is a voltage-gated ion-channel-forming peptide. Channels are generally considered to be formed by first insertion of amphipathic molecules into the phospholipid bilayer, followed by self-assembly of a variable number of transmembrane helices. We have studied the length of the peptide structure to address the question whether this peptide is long enough to span the phospholipid bilayer. The pulsed electron-electron double resonance (PELDOR) spectroscopic technique was used to determine the length of the helical molecule in membrane-mimicking solvents. This was achieved from the distance-related dipole-dipole interaction between spin labels, which were located at both ends of the linear peptide chain. The data were obtained by using samples of frozen glassy solutions of MeOH, MeOH/toluene, and MeOH/CHCl(3). Contributions of inter- and intramolecular interactions of spin labels were separated to analyze the intramolecular interaction and the distance distribution function between the labels. It is shown that the main maximum of the distribution functions is located at a distance of ca. 3.3 nm, and this distance appears to be only slightly dependent on the solvent composition. The distribution function was observed to narrow after addition of either CHCl(3) or toluene to MeOH. This effect is rationalized in terms of a decreased mobility of the terminal amino acid residues. By molecular-dynamics simulations, it was shown that the conformation, corresponding with the predominant distance found by PELDOR, agrees well with the mixed alpha/3(10)-helical that was previously determined by NMR. However, in the case toluene was added to the MeOH solution to further increase the hydrophobicity of the environment of the membrane-active peptide, the distribution function gives rise to a minor fraction (7-8%) with a distance of 4.2 nm. This distance corresponds most likely to the more extended 2(7)-helix structure.     

Product solutions and asymptotic behavior for age-dependent,dispersing populations

The paper presents some population models, containing both age structure and diffusion, for which there are stable age distributions. This means distributions which are products of functions of age only with functions of space and time only. For these models a formal calculation is presented showing that the stable distributions will always be the large-time limits. Two kinds of diffusion are studied: random, and directed (which means diffusion to avoid crowding). The principal specialization of the age structure is that the death modulus can be decomposed into the sum of two terms. The first is a function of age only and represents deaths by natural causes, while the second is a function of total population only and represents environmental effects.     

Evolution of senescence: Influence of age-dependent death rates on the natural increase of a hypothetical population

A hypothetical population is characterized by functions of age which describe its longevity and its maternity rate. Solution of the renewal equation for the birth rate of the population yields a characteristic equation which, in contradiction to the results of previous studies, may have more than one real root. The largest real root of the characteristic equation is the rate of natural increase, r, of the population and is used as a measure of its selective advantage.The maternity rate is represented by a rising or falling exponential function of age. Longevity is represented by a series each term of which has the form of a gamma distribution function. As the number of terms increases, the mean longevity remains constant, but the function becomes progressively more rectangular in shape; the early death rate declines, while the death rate in old age increases. Unless the reproductive fraction is small, each such decrease in the youthful death rate more than compensates for the corresponding increase in old age and causes an increment in r which is interpreted as a step toward the evolution of senescence. Although the degree of change in r attendant upon a change in the age-dependency of the death rate is related to the initial value of the maternity function, it is not influenced by the age dependency of the maternity function.     

A novel generalized normal distribution for human longevity and other negatively skewed data

Negatively skewed data arise occasionally in statistical practice; perhaps the most familiar example is the distribution of human longevity. Although other generalizations of the normal distribution exist, we demonstrate a new alternative that apparently fits human longevity data better. We propose an alternative approach of a normal distribution whose scale parameter is conditioned on attained age. This approach is consistent with previous findings that longevity conditioned on survival to the modal age behaves like a normal distribution. We derive such a distribution and demonstrate its accuracy in modeling human longevity data from life tables. The new distribution is characterized by 1. An intuitively straightforward genesis; 2. Closed forms for the pdf, cdf, mode, quantile, and hazard functions; and 3. Accessibility to non-statisticians, based on its close relationship to the normal distribution.     

海岱地区大汶口文化时期人口死亡年龄的统计分布特征

人口死亡年龄是揭示一个族群健康状况和社会经济条件的重要指标。本文根据海岱地区大汶口文化时期九个墓地人骨遗存的发掘报告,运用定量统计的方法检验了人口死亡年龄分布特征。发现该区大汶口文化时期人口的死亡年龄分布近似服从正态分布。最后探讨了造成人口低死亡年龄的可能原因,并给出了这一概率分布的数学意义以及在史前人口学中的应用前景。     

Childhood overweight in the United States: A quantile regression approach

The prevalence of overweight children in the United States has increased dramatically over the past two decades, and is creating well-known public health problems. Moreover, there is also evidence that children who are not overweight are becoming heavier. We use quantile regression models along with standard ordinary least squares (OLS) models to explore the correlates of childhood weight status and overweight as measured by the Body Mass Index (BMI). This approach allows the effects of covariates to vary depending on where in the BMI distribution a child is located. Our results indicate that OLS masks some of the important correlates of child BMI at the upper and lower tails of the weight distribution. For example, mother's education has no effect on black children, but is associated with improvements in BMI for overweight white boys and underweight white girls. Conversely, mother's cognitive aptitude has no effect on white boys, but is associated with BMI improvements for underweight black children and overweight white girls. Further, we find that underweight white children and black girls experience similar improvements in BMI as they get older, but that for black boys there is little if any association between age and BMI anywhere in the BMI distribution.     

Constitution and By-Laws of the American Association of Physical Anthropologists

From parent populations (N = 50,000) statistically generated, representing different levels of correlation (r) between the age at death and a hypothetical biological indicator (r = 0.8-0.98), reference samples and target demographic samples are randomly drawn. Two iterative techniques, proportional fitting procedure and Bayesian, are used to estimate from the reference samples the age distribution of the targets. Due to the random fluctuations of the pattern of aging, both in the reference and target samples, these techniques converge only in expectation toward the true value of a distribution, but not in practice for any particular realization. Nevertheless, these techniques allow the estimation of the average of an age distribution, even if its shape is unknown. Under the hypothesis that the target sample is drawn from a stationary population, this average represents the life expectancy at 20 years (plus 20 years). Using this mean age at death for the adults and the juvenility index at death (D5-14/D20-ω), a new set of paleodemographic estimators were derived from 40 archaic life tables. For a hypothesized stable population, they give the life expectancy at birth and at 20 years, and the probability of death at 1 and 5 years. © 1996 Wiley-Liss, Inc.     

Depth,contrast and view-based homing in outdoor scenes

Panoramic image differences can be used for view-based homing under natural outdoor conditions, because they increase smoothly with distance from a reference location (Zeil et al., J Opt Soc Am A 20(3):450–469, 2003). The particular shape, slope and depth of such image difference functions (IDFs) recorded at any one place, however, depend on a number of factors that so far have only been qualitatively identified. Here we show how the shape of difference functions depends on the depth structure and the contrast of natural scenes, by quantifying the depth- distribution of different outdoor scenes and by comparing it to the difference functions calculated with differently processed panoramic images, which were recorded at the same locations. We find (1) that IDFs and catchment areas become systematically wider as the average distance of objects increases, (2) that simple image processing operations—like subtracting the local mean, difference-of-Gaussian filtering and local contrast normalization—make difference functions robust against changes in illumination and the spurious effects of shadows, and (3) by comparing depth-dependent translational and depth-independent rotational difference functions, we show that IDFs of contrast-normalized snapshots are predominantly determined by the depth-structure and possibly also by occluding contours in a scene. We propose a model for the shape of IDFs as a tool for quantitative comparisons between the shapes of these functions in different scenes.     

不同年龄女性急性ST段抬高型心肌梗死患者冠状动脉病变特点、PPCI治疗临床疗效的差异及院内死亡的危险因素分析

摘要 目的：分析不同年龄女性急性ST段抬高型心肌梗死（STEMI）患者冠状动脉病变特点、经急诊经皮冠状动脉介入（PPCI）治疗后的临床疗效差异及院内死亡的危险因素。方法：选取2018年1月~2022年3月期间在我院接受PPCI治疗的女性STEMI患者408例,根据患者不同的发病年龄将其分为A组（年龄≤65岁,n=161）与B组（年龄>65岁,n=247）。对比不同的发病年龄PPCI冠状动脉病变特点、治疗后的临床疗效差异及院内不良事件发生情况。单因素和多因素Logistic回归分析女性STEMI患者院内死亡的危险因素。结果：A组、B组的病变血管数量、钙化病变组间对比有统计学差异（P<0.05）。A组、B组的病变血管部位、术前TIMI血流分级、分叉病变组间对比无统计学差异（P>0.05）。两组主动脉内囊反搏术比例组间对比未见明显差异（P>0.05）,B组症状发生到血管开通时间（S-to-D）、门-球囊扩张时间（D-to-B）时间长于A组（P<0.05）。两组术中死亡、支架内血栓、BARC3~5级出血比例组间对比无统计学差异（P>0.05）。B组术后死亡的发生率低于A组（P<0.05）。根据患者不同的预后结局分为存活组（n=369）和死亡组（n=39）。单因素分析结果显示女性STEMI患者院内死亡与年龄、糖尿病、体质量指数（BMI）、Killip心功能分级、术前TIMI血流分级、术后TIMI血流分级、住院天数、S-to-D时间、D-to-B时间、收缩压（SBP）、舒张压（DBP）、白细胞计数（WBC）、中性粒细胞、血小板体积分布宽度（PDW）、左心室射血分数（LVEF）、肌酸激酶同工酶（CK-MB）有关（P<0.05）。多因素Logistic回归分析,结果显示年龄偏大、LVEF偏低、CK-MB偏高、术后TIMI血流分级0~I级、S-to-D时间偏长是女性STEMI患者院内死亡的危险因素（P<0.05）。结论：不同年龄女性STEMI患者冠状动脉病变特点、且PPCI 的治疗效果存在一定的差异。此外,年龄偏大、LVEF偏低、CK-MB偏高、术后TIMI血流分级0~I级、S-to-D时间偏长是女性STEMI患者院内死亡的危险因素。     

Estimating and comparing the distribution of onset of disease from prevalence case-control data

Age at ascertainment from prevalence case-control data identifies the age-specific odds of disease. When age at onset is available from the cases, the conditional distribution of age at onset, given that disease occurs, is identifiable. Combining both kinds of information by introducing a multiplicative intercept allows identification of the marginal distribution of age at onset. Here, the approach is extended to the two-sample setting through a generalization of the multiplicative intercept model. The efficiency of the approach is explored and a test statistic based on the integrated difference between distribution function estimates is proposed. An approach to regularization of the likelihood is discussed. The methods are illustrated through an application to data on colorectal polyps obtained from a case-control study of individuals undergoing colonoscopy.     

Semiparametric method for estimating paleodemographic profiles from age indicator data.

This paper addresses the problem of estimating an age-at-death distribution or paleodemographic profile from osteological data. It is demonstrated that the classical two-stage procedure whereby one first constructs estimates of age-at-death of individual skeletons and then uses these age estimates to obtain a paleodemographic profile is not a correct approach. This is a consequence of Bayes' theorem. Instead, we demonstrate a valid approach that proceeds from the opposite starting point: given skeletal age-at-death, one first estimates the probability of assigning the skeleton into a specific osteological age-indicator stage. We show that this leads to a statistically valid method for obtaining a paleodemographic profile, and moreover, that valid individual age estimation itself requires a demographic profile and therefore is done subsequent to its construction. Individual age estimation thus becomes the last rather than the first step in the estimation procedure. A central concept of our statistical approach is that of a weight function. A weight function is associated with each osteological age-indicator stage or category, and provides the probability that a specific age indicator stage is observed, given age-at-death of the individual. We recommend that weight functions be estimated nonparametrically from a reference data set. In their entirety, the weight functions characterize the relevant stochastic properties of a chosen age indicator. For actual estimation of the paleodemographic profile, a parametric age distribution in the target sample is assumed. The maximum likelihood method is used to identify the unknown parameters of this distribution. As some components are estimated nonparametrically, one then has a semiparametric model. We show how to obtain valid estimates of individual age-at-death, confidence regions, and goodness-of-fit tests. The methods are illustrated with both real and simulated data.     

Spending patterns of Chinese parents on children's backpacks support the Trivers-Willard hypothesis: Results based on transaction data from China's largest online retailer

Using the 2015 student backpack transaction data from the largest E-commerce business in China, this study takes a novel “big data” approach to test the patterns of parental sex preference by comparing the difference in cost between blue and pink backpacks at different quantiles of the backpack cost distribution. Unconditional quantile regression results show that, depending on the quantile of choice, the blue-pink difference in backpack cost can be positive, negative, or zero. This indicates the presence of son preference, daughter preference, and gender indifference in the same population. Treating backpack cost as a proxy measure of parental economic status, such results indicate that parents of high economic status invest more heavily in sons whereas parents of low economic status invest more heavily in daughters, as predicted by the Trivers-Willard hypothesis. The discovery of a third group, between the high- and low-status parents, who invest equally in sons and daughters further strengthens the argument.     

Detection of significant demographic differences between subpopulations of prehispanic Maya from Copan, Honduras, by survival analysis

Heterogeneity and small sample size are problems that affect many paleodemographic studies. The former can cause the overall distribution of age at death to be an amalgam that does not accurately reflect the distributions of any of the groups composing the heterogeneous population. The latter can make it difficult to separate significant from nonsignificant demographic differences between groups. Survival analysis, a methodology that involves the survival distribution function and various regression models, can be applied to distributions of age at death in order to reveal statistically significant demographic differences and to control for heterogeneity. Survival analysis was used on demographic data from a heterogeneous sample of skeletons of low status Maya who lived in and around Copan, Honduras, between A.D. 400 and 1200. Results contribute to understanding the collapse of Classic Maya civilization.